Femtocells and other types of small cell base stations can be used to extend the coverage of a network provider's network by providing small base stations that can be installed in a user's home or office. The femtocells can help to solve capacity problems of the macro network as demand for voice and data services increases.
Femtocells and other types of small cell base stations may include a Network Listen (NL) Module that includes some mobile-station-like capabilities that allow the NL module to detect downlink control signals from a neighboring base station having a coverage area in which the small cell base station is located. The NL module can be configured to receive Over-the-Air (OTA) signals from neighboring base stations. The NL module can be configured to listen for and decode the OTA signals transmitted by neighboring base stations to obtain relevant information from one or more networks proximate to the base station that includes the NL module. The NL module can be configured to enable the base station to execute applications, including, but not limited to: (a) self-organizing network (SON) related applications, such as building a neighbor list, physical cell identity (PCI) selection to avoid PCI collisions with neighboring cells; (b) approximate location determination using cell global identity (CGI) of neighboring base stations; (c) time and frequency synchronization; and (d) interference management. The NL module of a small cell base station can be configured to listen for OTA signals from a neighboring base station and can be configured to use these signals from neighboring base station, such as a macrocell base station or even another small cell base station.
With respect to time and frequency synchronization, the NL listen module can enable a small cell base station to correct for timing and/or frequency synchronizations at the small cell base station. Some conventional base stations are configured to advertise the synchronization capability of the base station in terms of a relative ranking, referred to as a synchronization stratum. A small cell base station that includes a NL module can determine whether a neighboring base station has a tighter synchronization capability than the small cell base station based on the synchronization capability information advertised by the neighboring base station. Base stations having a lower stratum level, which implies that the base station has looser synchronization accuracy, can be configured to listen to control signals from base stations advertising a higher stratum level, and thus, tighter synchronization accuracy. The NL module of a small cell base station can thus be configured to select a neighboring base station advertising a higher stratum level. For example, a small cell base station may have a neighboring picocell, a neighboring macrocell base station, and a neighboring femtocell from which the small cell base station from which the small cell base station could obtain synchronization information. Macrocell base stations and picocells typically have tighter synchronization requirements than a femtocell, and may advertise be associated with a higher synchronization stratum level than the femtocell. However, in some femtocell implementations may have a higher synchronization level. For example, some femtocells may be configured to derive synchronization from reliable external sources, such as a Global Navigation Satellite System (GNSS) including the Global Positioning System (GPS) or from a network server using Precision Timing Protocol (PTP). Accordingly, a femtocell (or other small cell base station) may be associated with a high stratum level.